1. Field of the Invention
The present invention relates to a production method of silver halide photographic emulsion in which reaction, mixing or the like in a production process of silver halide photographic emulsion is carried out by a chemical unit operation, and a production apparatus thereof.
2. Description of the Related Art
In general, a silver halide photographic emulsion used for a photosensitive material is produced through a pre-ripening process in which a nucleus forming process (formation of a microcrystal dispersion of silver halide in protective colloid), a physical ripening process (crystal growth for obtaining a desired grain shape and size), and a crystal growth process are performed to form silver halide photographic emulsion grains having an objective size, shape and structure, a desalting process (removal of soluble salts from the dispersion), a sensitizing process (heat treatment performed in the presence of a sensitizing agent, for increasing sensitivity to light) for increasing the sensitivity of the emulsion after desalting, and a after-ripening process for adding various agents (sensitizing dye, stabilizing agent, and etc.) for giving various properties to the emulsion required as the need arises.
Incidentally, in the foregoing production process of the silver halide photographic emulsion, two or more processes among these processes, may be combined and carried out in one operation. Further, in the foregoing production process, one or more production stages may be omitted from the production process. Furthermore, there is also a case where plural operations are repeated in each stage in order to obtain a desired emulsion.
In addition, in a production system for industrially mass-producing silver halide emulsion, a so-called batch type production system using a large capacity reaction container is usually used.
As a conventional batch-type production system for producing silver halide emulsion, there is proposed one using a tank 10 as a reaction container as exemplified in FIG. 37 (for example, see JP-A No. 5-173267).
This tank 10 is constituted as a batch type reaction container apparatus having an agitator capable of producing of silver halide photographic emulsion at a time in a predetermined large amount, for example, 1000 l (1 t).
In this tank 10, in order to agitate a solution with which the tank is filled, a magnetic agitation means 16 is provided such that an agitation vane 12 is rotatively driven through a transmission means 14 for transmitting a rotation driving force of a motor 15 in a non-contact manner by using a magnetic force.
In addition, in order to perform a temperature control of the solution with which the tank is filled, a temperature control means 18 for heating or cooling the reaction solution is disposed at the outer peripheral part of the tank 10. The temperature control means 18 is constituted by use of means for heating or cooling by allowing a heat exchange medium (water, water vapor, liquid organic material, flame gas, etc.) to flow to a temperature control part, or a means for performing a temperature control by installing an element for electrically heating or cooling at the temperature control part.
The tank 10 is constituted to be capable of being hermetically closed by mounting a sealing lid 20 to the tank 10. Further, an emulsion introduction pipe 22 with an opening and closing cock is disposed in the sealing lid 20 of the tank 10. Furthermore, a liquid transfer pipe 24 with an opening and closing cock is disposed at the bottom of the tank 10.
In the butch type production system using this tank 10, at the nucleus forming process in the pre-ripening process at the time of producing a silver halide emulsion, a predetermined quantity of an aqueous dispersion medium solution containing at least a dispersion medium and water is injected through the emulsion introduction pipe 22 into the tank 10, and further, a silver salt solution or a silver salt solution and a halide solution are added under the conditions of pBr 2.5 or less and are agitated by the magnetic agitation means 16 for a predetermined time (several minutes), and temperature is controlled by means of a temperature control means 18 so as to keep the reaction solution in the tank 10 within a predetermined temperature range (for example, 5° C. to 45° C.), so that nuclei of minute tabular grains including, for example, a parallel twinning plane are formed.
In this nucleus forming process, since solute ions are randomly walking in the solution when the nuclei are formed, minute tabular grain nuclei and a large number of other minute grains (especially, non-twin, single twin, or non-parallel double twin grains) are simultaneously formed in the tank 10.
Next, in the butch-type production system using this tank 10, at the ripening process in the pre-ripening process at the time when the silver halide photographic emulsion is produced, grains other than the tabular grain nucleus are made to disappeared by the Ostwald ripening process, and the tabular grain nucleus is made to grow.
In this ripening process, three ripening methods that have conventionally been used described below can be used. The first type of the ripening method is a method in which after nucleus formation, a pBr value of the reaction solution in the tank 10 is adjusted to 2.5 to 1.0, preferably 2.3 to 1.4, a solvent for AgX is added through the emulsion introduction pipe 22 (AgNO3 may be added during the ripening), agitation is performed by the magnetic agitation means 16, and the temperature of the reaction solution in the tank 10 is raised by the temperature control means 18 by preferably 10° C. or higher, more preferably 20° C. or higher with respect to the nucleus formation temperature, sob that ripening is performed for predetermined several minutes or more.
The second type of the ripening method is a method in which after nucleus formation, a pBr value of the solution is adjusted to 2.5 or less, preferably 1.0 to 2.0, a first ripening is performed for predetermined several minutes or more in a state where there is no solvent for AgX, and next, AgNO3 is added through the emulsion introduction pipe 22 to increase the pBr value by 0.1 or more, preferably 0.3 or more, the solvent for AgX is added through the emulsion introduction pipe 22, agitation is performed by the magnetic agitation means 16, and the temperature of the reaction solution in the tank 10 is raised by the temperature control means 18 by preferably 10° C. or higher, more preferably 20° C. or higher with respect to the nucleus formation temperature, so that second type of ripening is performed for predetermined several minutes or more.
The third type of ripening method is a method in which after nucleus formation, a pBr value of the solution is adjusted to 2.5 or less, preferably 1.0 to 2.0, agitation is performed by the magnetic agitation means 16 in a state where there is no solvent for AgX, the temperature of the reaction solution in the tank 10 is raised by the temperature control means 18 by preferably 10° C. or higher, more preferably 20° C. or higher with respect to the nucleus formation temperature, so that the third type of ripening is performed for predetermined several minutes or more. Incidentally, there is also a method in which AgNO3 is added during the ripening.
Further, in the foregoing first to third type of ripening methods, there is also a method using a pressure ripening method in which the tank 10 is made a hermetically sealed system only at the time of ripening, and ripening is performed in a state where the pressure in the tank 10 at the time of nucleus ripening is more than several times as high as the atmospheric pressure. Further, there is also a method in which the ripening is performed by the foregoing first to third ripening methods in the presence of an anti-fogging agent.
Next, in the batch type production system using this tank 10, after the ripening process in the pre-ripening process at the time of production of the silver halide emulsion has been ended, tabular grain nuclei are made to grow in the crystal growth process.
In the crystal growth process, it is possible to use a method of adding a silver salt solution and a halide solution as a solute for growing a crystal of tabular grain nuclei, a flow acceleration addition method, a concentration acceleration addition method, and a combined addition method of two or more of these methods.
In the batch type production system using this tank 10, also at the crystal growth stage in the pre-ripening process at the time of production of the silver halide emulsion, a predetermined quantity of silver salt solution and halide solution as solutes for growing the crystals of the tabular grain nuclei is injected from the emulsion introduction pipe 22 into the reaction solution stored in the tank 10, agitation is performed by the magnetic agitation means 16 for a predetermined time (several minutes), a temperature control is performed by the temperature control means 18 to bring the reaction solution in the tank 10 to a predetermined temperature, and a chemical reaction for suitably allowing to grow crystals is accelerated (see, for example, Japanese Patent Application Nos. 2-142635 and 2-43791).
In the batch type production system using this tank 10, after the crystal growth process in the pre-ripening process at the time of production of the silver halide emulsion has been ended, the desalting process is carried out.
The desalting process is a process of removing unnecessary materials (for example, K, Na) formed during the emulsion grain formation of the pre-ripening process, excessively existing ions (for example, Ag, Br, Cl) and the like.
In the desalting process, various desalting methods, such as a flocculation method or a noodle washing method in which water washing is performed to effect desalting, or an ultrafiltration or an electrodialysis method in which desalting is carried out by separation (film), can be used.
In the desalting process, for example, in the case where the flocculation method is used, the reaction solution which has been subjected to the pre-ripening process in the tank 10 as shown in FIG. 37 is taken out from the liquid transfer pipe 24, and is transferred to a desalting tank (not-show), and a flocculant is added to the reaction solution in the desalting tank, and a pH value of the solution is adjusted, so that emulsion grains together with gelatin, are flocculating-sedimented (natural sedimentation), a supernatant liquid containing unnecessary materials is removed, and next, after washing water is newly added into the desalting tank, the flocculation of gelatin is deflocculated by adjusting pH value of the solution. These processes are repeated two or three times.
Further, in this batch type production system, after the desalting process at the time of production of the silver halide emulsion has been ended, an after-ripening process is carried out. This after-ripening process is a process in which the emulsion having a low sensitivity in the reaction solution after desalting process is sensitized to impart sensitivity suitable for practical use.
In the sensitizing method at the after-ripening process in the batch type production system, there are a chemical sensitizing method and a spectral sensitizing method. The chemical sensitizing method is a method for increasing the intrinsic sensitivity of the emulsion. A typical chemical sensitizing method includes three kinds of methods, that is, a sulfur sensitizing method, a gold sensitizing method and a reduction sensitizing method.
In the case where this chemical sensitizing method is performed, the reaction solution which has been subjected to the desalting process is transferred to a tank as a reaction container (not-shown) constituted similarly to the foregoing tank 10, a chemical sensitizing agent is metered and a predetermined quantity of the agent is added through an agent introduction pipe to the reaction solution stored in the tank. An agitation vane stirs the solution, and the temperature of the solution is controlled by a temperature control means so that the chemical sensitizing agent is uniformly distributed to emulsion grains to complete a desired chemical reaction equally.
In addition, the spectral sensitizing method as the sensitizing method in the after-ripening process is a method in which in the case where the emulsions are used in a color photosensitive material or the like, sensitizing wavelength ranges are respectively widened into the wavelength ranges of the three primary colors of light, that is, blue (400 to 500 nm), green (500 to 600 nm), and red (600 to 700 nm) from the intrinsic sensitivities of the emulsions in the reaction solutions.
The spectral sensitizing method is generally performed by adsorbing a sensitizing dye onto an emulsion. As the sensitizing dye used here, there is an orthochromatic sensitizing dye (for green) or a panchromatic dye (for red). The sensitizing dyes are dissolved in methanol to form a solution, or are made a dye solid dispersed solution in gelatin, and are added to the emulsion as the reaction solution.
Incidentally, the dye solid dispersed solution in gelatin is prepared at a preparation process, and is temporarily refrigerated, and at the time of use, it is melted to add to the emulsion.
When the spectral sensitizing method is used, the reaction solution which has been subjected to the desalting process is transferred to a tank as a reaction container (not-shown) constituted similarly to the foregoing tank 10, a solution in which a sensitizing dye is dissolved in methanol or a solution in which a sensitizing dye is made to a solid dispersed solution in gelatin (this solid dispersed solution in gelatin is prepared at a preparation process, is temporarily refrigerated, is melted at the time of use to be added to the emulsion) is metered and a predetermined quantity of solution is added through an agent introduction pipe to the reaction solution stored in the tank. The solution is stirred well by an agitation vane, the temperature of the solution is controlled by a temperature control means so that the chemical sensitizing agent is uniformly distributed to the emulsion grains and is uniformly adsorbed by the grains.
In this batch type production system, after the after-ripening process in the production processes of the silver halide emulsion has been completed, a storage process is performed. The storage process is a process of temporarily storing the emulsion prepared in the batch operation for the purpose of supplying the emulsion to an emulsion coating process in continuous operation.
Further, in addition to the function of temporal storage, this storage process also provides a function to stop the progress of ripening by cooling the emulsion to eliminate differences in characteristics among emulsion preparation batches by batch-blending a plurality of the same kind emulsions, as well as a function for quality assurance by measuring physical properties of the prepared emulsions to assure the characteristics of the emulsions.
Thus, in the batch type production system, the equipment for the storage process is constituted by a cooling apparatus, a blend tank, a storage apparatus and the like. The cooling apparatus for stopping the progress of ripening may be constituted by a heat exchange system using a plate type heat exchanger or the like, or by a vacuum cooling system for effecting cooling by utilizing latent heat of vaporization.
In this batch type production system, in order to perform the production process of the silver halide emulsion in one or plural stages, the tank 10 as the batch type reaction container device equipped with the agitator is used, and a plurality of chemicals in large amounts introduced into the tank 10 for producing an emulsion are forcibly mixed by a magnetic agitation means 16.
The tank 10 as the batch type reaction container device equipped with the agitator is suitable for production of a large quantity of emulsion. However, when another new liquid chemical is injected through the emulsion introduction pipe 22 to the chemicals for producing the emulsion stored in the tank 10, and a plurality of chemicals in a large amount introduced into the tank 10 are agitated by the agitation vane 12 and are mixed, the liquid chemicals newly injected through the emulsion introduction pipe 22 are stagnant in the vicinity of the injection port of the emulsion introduction pipe 22 or circulates in the tank 10.
Accordingly, in the initial state where a plurality of liquid chemicals in a large quantity for producing the emulsion are agitated by the agitation vane 12 to start mixing thereof, it is inevitable such a state that the liquid chemical newly injected through the injection port of the emulsion introduction pipe 22 is locally mixed at a high concentration into a part of the liquid chemicals for producing the emulsion stored in the tank 10 existing at a place where the chemicals are circulated in the tank 10, and a mixing concentration of the liquid chemicals becomes low at a portion which is remote from the injection port of the emulsion introduction pipe 22 and which the newly injected liquid chemical does not reach through the circulation by the agitation vane 12.
Accordingly, when a plurality of liquid chemicals in a large amount for producing an emulsion are stirred by the agitation vane 12, a difference in history of a chemical change arises between one where mixing of the newly injected liquid chemical is started at a high concentration thereof and one where mixing of the newly injected liquid agent is started at a low concentration thereof, so that the compounds formed become non-uniform in the entire tank 10.
Further, a non-uniform chemical reaction may occur due to a dead space existing in a small part in the tank 10, or due to variation in the liquid flow when the liquid chemicals for producing the emulsion is stirred by the agitation vane 12.
In addition, when the liquid chemicals in a large quantity for producing an emulsion in the tank 10 are heated by the temperature control means 18, since the temperature control means 18 heats the chemicals through the wall of the tank 10, there is a case where when a heating process is started, the liquid chemicals for producing the emulsion in the tank 10 are rapidly heated only at the place close to the wall of the tank 10, and the temperature is not raised at the center in the tank 10, so that the temperature distribution of the liquid chemicals for producing the emulsion in the tank 10 becomes uneven, a history difference in the chemical change, and compounds formed becomes non-uniform in the entire tank 10.
Furthermore, in the method of forming silver halide grains constituting the silver halide emulsion, which is industrially carried out today, there is a process in which a silver nitrate solution and a halide solution are added to a dispersion medium solution (protective colloid solution) typified by gelatin under vigorous agitation, and are mixed as quickly as possible to form silver halide grains.
In this silver halide grain forming process, since an ionic reaction in which a silver ion and a halogen ion react with each other to form silver halide is very rapid, it is essential to quickly agitate and mix these two ionic solutions in a short time in order to perform a uniform reaction.
Here, for example, in the case where nucleus formation is performed by a method in which a silver salt solution and a halide solution are added to a dispersion medium in the tank 10 from the emulsion introduction pipe 22 and are agitated by the agitation vane 12, a vortex is generated by the agitation vane 12 rotating at a high speed in the liquid chemicals for producing the emulsion in which the silver salt solution and the halide solution are added in the dispersion medium in the tank 10, and mixing by turbulent flow is carried out in the process in which the vortex is subdivided.
Even in this case, once the nuclei thus formed circulate in the tank 10 to cause a so-called local recycling, and at the same time as the formation of the nuclei, crystal growth from the nuclei occurs in parallel, so that it is difficult to form monodispersed nuclei.
Further, in the field of silver halide photography, a tabular silver halide grain having a large light receiving area is widely used as a photosensitive element. In order to increase a light receiving efficiency, a thin tabular silver halide grain is preferable.
However, in the batch type production system using the tank 10 and the agitation vane 12 mentioned above, when the agitation is performed by the agitation vane 12 to produce the silver halide emulsion, the tabular silver halide grains during the process of crystal growth pass through a high supersaturation region in the vicinity of the injection port of the emulsion introduction pipe 22 for adding silver ion or halide ion, and an adverse effect such that the thickness of the tabular grains increases is apt to occur.
Furthermore, in the batch type production system using the tank 10 and the agitation vane 12, on the assumption that the quantity of silver halide emulsion produced at one time in the tank 10 is a predetermined constant quantity, the shape of the agitation vane 12 is determined to obtain an appropriate agitating state in the tank 10. Accordingly, when a production scale is changed to produce a desired quantity of emulsion, there is a fear that the characteristics of the emulsion are changed, and the preparation scale cannot be changed. Therefore, a predetermined quantity of silver halide emulsion larger than a desired quantity of emulsion must be produced, and as a result, there is a drawback that the silver halide emulsion produced in an excess amount is wastefully discarded.
On the other hand, with respect to a newly prescribed silver halide emulsion developed by using an experimental apparatus, in the case where a small production system using the experimental apparatus is scaled up to a mass production system using a mass production apparatus, it is necessary to repeat trial production and product test many times in order to verify conditions under which the same characteristics as the emulsion characteristics obtained by the experimental apparatus for small production can be achieved in the newly prescribed silver halide emulsion produced by the production apparatus for mass production. Accordingly, there are problems that it takes a long time to develop the production system for mass production, and the loss of raw material consumed for the product test is large.
Furthermore, it has been proposed that a microreactor is used for a part of a production process of silver halide photographic emulsion used for photosensitive material (see, for example, Japanese Patent Application No. 2001-76564).
The microreactor used in this method is one of micro devices, in which a plurality of solutions introduce into each mixing space through microchannels having an equivalent diameter of several μm to several hundred μm having a cross-section when converted into a circle, to cause a chemical reaction.
In such a microreactor, two kinds of solutions are made to flow through fine liquid supply passages called microchannels and are supplied as very thin lamella-like laminar flows into the mixing space, so that the two kinds of solutions are mixed and are allowed to react with each other in the mixing space (see, for example, JP-W No. 9-512742, WIPO International Publication WO 00/62913).
In a fluid circuit used in such a microreactor, there is a case where it is required that three or more kinds of fluids are allowed to rapidly react with one another by the microreactor. However, the conventional microreactor is constituted such that two kinds of fluids are allowed to react with each other. Thus, in the case where three or more kinds of fluids are made to react with each other by the conventional microreactor, it is necessary that a fluid circuit is constituted such that two or more microreactors are connected in series by piping or the like, and three or more kinds of fluids are made to react with each other stepwisely by using this fluid circuit.
In such a fluid circuit, there is a limit in shortening a distance between a microreactor disposed at the upstream side and a microreactor disposed at the downstream side, a certain period of time is necessary to mix another fluid with two kinds of fluids in a reaction container to make to react with the fluids each other. Therefore, it is impossible to make to react with three kinds of fluids one another at the same time. Moreover, in the fluid circuit, as the kinds of fluids to be supplied are increased, the number of elements (microreactors) constituting the circuit is increased, so that the circuit structure becomes complicated. Incidentally, this applies in the case where three or more kinds of fluids are mixed at the same time.
In addition, in the conventional microreactor, plural liquid supply passages respectively have liquid supply ports facing a mixing space so as to open respective liquid supply openings, and solutions are introduced into the mixing space through these plural liquid supply ports. However, there exists a portion where the cross-section of the mixing space is abruptly enlarged with respect to the sum of the opening areas of these liquid supply ports, and there exists a portion in the mixing space where the direction of flow of solutions to be mixed is abruptly changed. The solutions are apt to stagnate in the vicinity of the portion where the cross-section is abruptly enlarged in this mixing space or in the vicinity of the portion where the direction of the flow of the solutions to be mixed is abruptly changed, and especially in the case where a reaction between solutions is a precipitation generation reaction accompanied by coalescence or growth, aggregation or deposition occurs in the stagnant part, and there is a fear that there occurs clogging due to this, or reduction of uniformity of a reaction product due to the mixture of aggregates or deposits.
Further, in the conventional microreactor, according to the kinds of solutions supplied to plural liquid supply passages, a time when these solutions are mixed or a time when the mixing of the solutions accompanying a chemical reaction is performed, (hereinafter referred to as “mixing time”) is changed. That is, as the viscosity of the solution becomes high, the mixing time becomes longer in general, and in the case where the aggregation or deposition occurs accompanying the chemical reaction between the solutions, the aggregates or deposits become an inhibiting factor of mixing, that is, causes the lowering of diffusing power to the solution, and the mixing time is changed.
In such a microreactor, since the passage length in the flow direction of the solutions in the mixing space is constant, in the case where the flow rate of the solutions is constant, a time (passing time) when the solutions pass through the mixing space becomes constant. Accordingly, in the case where the mixing time of the solutions in the mixing space is longer than the passing time, it is necessary to reduce the flow rate of the solutions in the mixing space, so that the processing rate of the solutions in the microreactor is lowered. At this time, in order to prevent the decrease in the process rate of the solution, it is conceivable to extend the passage length of the mixing space. However, in the case where such measures are taken, the microreactor is enlarged or the production cost is increased. Further, in the case where the passage length of the mixing space is extended more than needs, the aggregation, deposition or the like of the solution is promoted by contraries, the clogging occurs in the mixing space, and the maintenance of the microreactor becomes troublesome.
Accordingly, in the foregoing conventional microreactor, an actuator is coupled to a block-shaped mixer element in which liquid supply passages branching from a supply part of a solution in the shape of the teeth of a comb are formed, a mechanical vibration is given to the mixer element by this actuator, and the mixing of plural solutions is accelerated by this mechanical vibration.
However, in this conventional microreactor, the vibration is given to only the mixer element in which plural liquid supply passages are formed, and this vibration is transmitted to the solutions in the mixing space through the solutions in the liquid supply passages, so that the mixing of the solutions in the mixing space is accelerated. Thus, in such a microreactor, it is difficult to control the progress of the mixing of the solutions in the mixing space and the progress of the chemical reaction accompanying the mixing with high accuracy. For example, in the case where the chemical reaction between the solutions in the mixing space is desired to be performed stepwise, or in the case where the solution and reaction product are desired to be diffused and mixed over the whole length of the mixing space, it is difficult to realize such progress of the mixing or the chemical reaction.